During the invasion parachutists soon learned that they had difficulty finding their comrades and communicating without being found out by the enemy. Upon approach, a click would be made using the tool, and friendly troops would respond with two clicks of their own. The clicker provides a distinct click sound when the tin backer was depressed against the brass body of the small 2 inch device. The top has an indenture for the thumb, a key chain or lanyard hole, and a U.S. stamp. This little reproduction played an important part in saving the lives of our US paratroopers and is a great keepsake to have.